The rapid advances in electronic devices and electric automobiles are being accompanied by greater demand for increased capacity of secondary batteries, and non-aqueous electrolyte batteries, such as lithium ion secondary batteries with high energy densities, are widely used and are under active investigation.
The electrolyte solution used in non-aqueous electrolyte batteries is generally constituted primarily of an electrolyte salt and a non-aqueous solvent. A non-aqueous electrolyte solution provided by the dissolution of an electrolyte, e.g., LiPF6, in a mixed solvent of a high dielectric constant solvent, e.g., a cyclic carbonate, with a low-viscosity solvent, e.g., a chain carbonate, is used as an electrolyte solution in lithium ion secondary batteries.
When a lithium ion secondary battery undergoes repetitive charge/discharge, the battery capacity declines due to the occurrence of, for example, decomposition of the electrolyte at electrode surfaces, deterioration of the materials making up the battery, and so forth. In addition, depending on the case, the stability with respect to, e.g., battery swelling, rupture, and so forth, may also be reduced.
To date, methods have been proposed for improving the battery characteristics of lithium ion secondary batteries through the use of specific non-aqueous electrolyte solutions. For example, PTL 1 reports that the decline in charge/discharge performance associated with the battery swelling and increased internal impedance caused by decomposition of the electrolyte solution during the first charging cycle is suppressed by the incorporation, in the electrolyte solution or solid electrolyte, of tetrahydropyran or a derivative thereof. PTL 2 reports that—through the addition in a proportion of 0.001 to 0.1 mol/L of an organic compound having two or more cyano groups to an electrolyte solution in which a lithium salt is dissolved in a non-aqueous solvent—a Li secondary battery can be formed that has an excellent electromotive force, discharge capacity, and charge/discharge cycle life and that can be stably charged at high voltages in excess of 4.2 V. In addition, PTL 3 reports that—through the use of a non-aqueous electrolyte solution containing at least 25 volume % and not more than 40 volume % (25° C., 1 atm) ethylene carbonate and containing 1,3-dioxane and a dinitrile compound as additives—a non-aqueous electrolyte secondary battery is obtained that is capable of high-voltage charging and that exhibits excellent cycling characteristics and an excellent high-temperature storability.